Soft contact lenses, such as those made from plastic gel materials, e.g., hydroxyethyl methacrylate (HEMA) or its analogues and ethylene glycol dimethacrylate (EGMA) or its analogues, are replacing traditional hard contact lenses as the lenses of choice for many people. Soft lenses are more comfortable to wear than the hard lenses, but they pose a more complex problem than the hard lenses when it comes to care and maintenance. Hard lenses may be cleaned and disinfected relatively easily. Since they do not absorb appreciable amounts of water and aqueous solutions, the use of somewhat harsh cleaning and disinfecting agents is not generally a problem.
Soft lenses, on the other hand, require greater care in cleansing and storage. The solutions useful with hard lenses often are not compatible with soft lenses because the soft lenses tend to absorb or concentrate certain constituents of the formulation, which could result in damage to the lens or harm to the eye of the user.
Similarly, soft lenses are more vulnerable to microbial contamination than are hard lenses. The nutritive effect of body fluids, and the protective effect of nicks or imperfections in soft lenses, can serve to augment the growth of microbes.
While it is relatively easy to find antimicrobial agents active against such microbial contaminants, it is more difficult to find an antimicrobial agent that is compatible with soft contact lenses, and more difficult yet to find one that is non-irritating and safe for contact with the human eye.
Antimicrobial agents which are suitable for external contact or even for injection or ingestion are often unsuitable for use in eye care due to the particularly sensitive nature of the tissues in the eye. For example, they might be unsuitable because of direct toxicity to the eye, poor solubility in aqueous vehicles, eye irritation or ocular allergenic effects, absorption or binding by the contact lens, or chemical interaction with the contact lens or even its plastic lens case.
An antimicrobial agent useful for ocular applications must not contribute to any of the above problems. In particular, it must satisfy two basic requirements, i.e. that it be non-irritating to the eye, and that it be effective against a wide variety of microorganisms.
Hydrogen peroxide is a very effective antimicrobial agent which is currently used to disinfect contact lenses, including soft contact lenses. Although it is potentially irritating to the eye if significant residues are contained on or in the contact lens, it is known that hydrogen peroxide can be removed by soaking a disinfected lens in a solution containing a catalyst such as platinum oxide which catalyzes the decomposition of hydrogen peroxide. Solutions of the enzyme catalase have also been added to decompose hydrogen peroxide in solutions previously used to sterilize contact lenses. See, for example, European Patent application No. 82710055.3. However, if introduced into a solution with a lens, catalase can bind to the lens, compounding the familiar protein deposit problem associated with the use of contact lenses.
It is known in the art that certain proteins can be immobilized on specific supports. U.S. Pat. No. 4,098,645 describes the immobilization of enzymes on isocyanate end-capped polyurethane polymer foams, and catalase is one of a long list of enzymes listed and claimed.
U.S. Pat. No. 3,282,702 describes certain classes of polymeric carriers which bind catalase for the purpose of providing articles for removing hydrogen peroxide from potable liquids.
U.S. Pat. No. 4,210,722 describes a method of immobilizing a protein such as an enzyme on a polar support in a variety of configurations which may be glass, ceramic, inorganic oxide, etc. comprising applying a layer of a polymer having repeating units containing a beta-hydroxy-alkyleneamine moiety such as the dimethylamine adduct of epoxidized polybutadiene to a polar support and contacting the treated support with an aqueous solution of the protein. One of the enzymes exemplified in this patent is catalase.